/*
 * Convert a color from RGB specification to HLS specification
 *
 * The code in this file includes:
 *
 *	The program described in figure 13.36, page 595 of:
 *		_Computer Graphics: Principles and Practice_,
 *		2nd edition, (1990),  by
 *		J.D. Foley, A. van Dam, S.K. Feiner, and J.F. Hughes
 *		Addison-Wesley Publishing Company
 *		ISBN: 0-201-12110-7
 *
 */

/*  HISTORY:
 *	Date     Pro Spec Rev	Prgmr	Description
 *	-------	 ------------	-----	-----------
 *	03Jan91  		tbb	Initial implementation as per the text.
 */

#include "stdio.h"
#include "ctype.h"
#include "math.h"

#define ML_MIN(a,b)	(((a)<(b))?(a):(b))
#define ML_MAX(a,b)	(((a)>(b))?(a):(b))


static void
aux_rgb_to_hls (r, g, b, h, l, s)
     float *r;			/* IN Red value		(0.0 <= r <= 1.0) */
     float *g;			/* IN Green value	(0.0 <= g <= 1.0) */
     float *b;			/* IN Blue value	(0.0 <= b <= 1.0) */
     float *h;			/* OUT Hue 		(0.0 <= h < 360.0)*/
     float *l;			/* OUT Lightness	(0.0 <= l <= 1.0) */
     float *s;			/* OUT Saturation	(0.0 <= s <= 1.0) */
 /*
  * If s == 0, then h is undefined.
  *
  * The procedure described in Foley & van Dam places red at 0 degrees of
  * hue angle, whereas DIGITAL VT3xx terminals place blue at 0 degrees.
  * This routine has blue at 0 degrees.
  */
{
/* Reference: figure 13.36, page 595 of Foley & van Dam */
    float maxval;
    float minval;
    float delta;

    maxval = ML_MAX (*r, ML_MAX (*g, *b));
    minval = ML_MIN (*r, ML_MIN (*g, *b));

    *l = (maxval + minval) / 2.0;	/* This is the lightness value. */

    if (maxval == minval)
    {
	/*
	 * Achromatic case, because r==g==b
	 */
	*s = 0.0;
	*h = -1.0;		/* The Hue is UNDEFINED in this case. */
    }
    else
    {
	/*
	 * Chromatic case.
	 */
	/* Calculate the saturation. */
	if (*l <= 0.5)
	{
	    *s = (maxval - minval) / (maxval + minval);
	}
	else
	{
	    *s = (maxval - minval) / (2.0 - maxval - minval);
	}

	/* Calculate the hue. */
	delta = maxval - minval;
	if (*r == maxval)
	{
	    /* The resulting color is between yellow and magenta. */
	    *h = (*g - *b) / delta;
	}
	else
	{
	    if (*g == maxval)
	    {
		/* The resulting color is between cyan and yellow. */
		*h = 2.0 + (*b - *r) / delta;
	    }
	    else
	    {
		if (*b == maxval)
		{
		    /* The resulting color is between magenta and cyan. */
		    *h = 4.0 + (*r - *g) / delta;
		}
	    }
	}

	*h = *h * 60.0;		/* Convert to degrees */

	*h = *h - 240.0;	/* Subtract to shift from Red at */
	/* zero hue to Blue at zero hue. */

	while (*h < 0.0)
	{			/* Be sure 0.0 <= hue <= 360.0 */
	    *h = *h + 360.0;
	}
	while (*h > 360.0)
	{
	    *h = *h - 360.0;
	}

    }				/* End else Chromatic case.*/

}				/* End of aux_rgb_to_hls routine. */


int
main (argc, argv)
     int argc;
     char **argv;
{
    float red, green, blue;
    float hue, lightness, saturation;

    /* Test cases */
    /* Convert BLUE */
    red = (float) 0x00;
    green = (float) 0x00;
    blue = (float) 0xFF;

    (void) fprintf (stdout, "\nInput  RGB value is: %X%X%X\n",
		    (int) red, (int) green, (int) blue);

    red = red / 0xFF;		/* Convert to percentages. */
    green = green / 0xFF;
    blue = blue / 0xFF;

    aux_rgb_to_hls (&red, &green, &blue, &hue, &lightness, &saturation);

    (void) fprintf (stdout,
	    "Output HLS value is: Hue = %f Lightness = %f Saturation =%f\n",
		    hue, lightness, saturation);

    /* Convert RED */
    red = (float) 0xFF;
    green = (float) 0x00;
    blue = (float) 0x00;

    (void) fprintf (stdout, "\nInput  RGB value is: %X%X%X\n",
		    (int) red, (int) green, (int) blue);

    red = red / 0xFF;		/* Convert to percentages. */
    green = green / 0xFF;
    blue = blue / 0xFF;

    aux_rgb_to_hls (&red, &green, &blue, &hue, &lightness, &saturation);

    (void) fprintf (stdout,
	    "Output HLS value is: Hue = %f Lightness = %f Saturation =%f\n",
		    hue, lightness, saturation);

    /* Convert GREEN */
    red = (float) 0x00;
    green = (float) 0xFF;
    blue = (float) 0x00;

    (void) fprintf (stdout, "\nInput  RGB value is: %X%X%X\n",
		    (int) red, (int) green, (int) blue);

    red = red / 0xFF;		/* Convert to percentages. */
    green = green / 0xFF;
    blue = blue / 0xFF;

    aux_rgb_to_hls (&red, &green, &blue, &hue, &lightness, &saturation);

    (void) fprintf (stdout,
	    "Output HLS value is: Hue = %f Lightness = %f Saturation =%f\n",
		    hue, lightness, saturation);



    /* End of test cases: */
    /* Convert terra cotta (0xC86446) */
    red = (float) 0xC8;
    green = (float) 0x64;
    blue = (float) 0x46;

    (void) fprintf (stdout, "\nInput  RGB value is: %X%X%X\n",
		    (int) red, (int) green, (int) blue);

    red = red / 0xFF;		/* Convert to percentages. */
    green = green / 0xFF;
    blue = blue / 0xFF;

    aux_rgb_to_hls (&red, &green, &blue, &hue, &lightness, &saturation);

    (void) fprintf (stdout,
	    "Output HLS value is: Hue = %f Lightness = %f Saturation =%f\n",
		    hue, lightness, saturation);

    /* Convert gray (0xAAAA96)*/
    red = (float) 0xAA;
    green = (float) 0xAA;
    blue = (float) 0x96;

    (void) fprintf (stdout, "\nInput  RGB value is: %X%X%X\n",
		    (int) red, (int) green, (int) blue);

    red = red / 0xFF;		/* Convert to percentages. */
    green = green / 0xFF;
    blue = blue / 0xFF;

    aux_rgb_to_hls (&red, &green, &blue, &hue, &lightness, &saturation);

    (void) fprintf (stdout,
	    "Output HLS value is: Hue = %f Lightness = %f Saturation =%f\n",
		    hue, lightness, saturation);

}				/* End of main RGB2HLS.C routine.*/